This invention relates to a connecting structure of bulb used in a headlamp of, a tail lamp and meters of a vehicle.
So-called wedge base-type bulbs, having no metal base, have been extensively used as electric bulbs serving as a light source for a headlamp, a tail lamp and meters. Such bulbs have now become a mainstream. A base portion of the wedge base-type bulb is inserted into a socket, and this socket is connected to a mating connector or the like, so that the wedge base-type bulb is supplied with electric power from a battery.
The wedge base-type bulb is not provided with a metal base, and therefore lead wires, connected to filaments, are connected to relay terminals provided in the socket, and these relay terminals are connected respectively to terminals received in the connector, thereby forming an illumination circuit. FIG. 7 shows one such known connecting structure of bulb disclosed in JP-A-9-55272.
As shown in the drawing, an electric bulb 100 is a wedge base-type bulb 100 having two filaments 101. The bulb 100 has a generally-flattened base portion 103 formed at a lower end of a silica glass tube 102, and lead wires 104 extend outwardly through the lower end of the base portion 103. End portions of the lead wires 104 are directed away from each other in a direction of a thickness of the base portion 103, and are folded back toward the silica glass tube 102 to extend respectively along opposite sides of the base portion 103 to form contact piece portions 104a, respectively.
A socket 105 includes a socket body 106, and relay terminals 109. The socket body 106 has a bulb mounting portion 107 having an opening for mounting the bulb 100 therein. Relay terminals 109 are mounted on an inner face of the bulb mounting portion 107. Terminal portions 109a of the relay terminals 109 are connected respectively to terminals of a connector (not shown) to supply electric power from a battery (not shown) to the bulb 100.
When the bulb 100 is mounted on the bulb mounting portion 107, retaining portions 103a on the base portion 103 are engaged respectively with resilient retaining pieces 108 formed on the bulb mounting portion 107, thereby preventing the bulb 100 from withdrawal from the socket 105. The base portion 103 is sandwiched between the relay terminals 109, and at the same time the contact piece portions 104a contact the relay terminals 109, respectively.
However, the above related connecting structure of bulb has the following problems to be solved.
Firstly, the lead wires 104, extending outwardly through the lower end of the base portion 103, must be folded back toward the silica glass tube 102 to form the contact piece portions 104a, and therefore there is a problem that additional time and labor are required for processing the end portions of the lead wires 104.
And besides, the structure of the socket 105 is complicated since this socket 105 includes the socket body 106 and the relay terminals 109. There is a problem that the cost increases. The relay terminals 109 are not fixed to the inner face of the bulb mounting portion 107, but are merely disposed along this inner face, and therefore there is a fear that the relay terminals 109 are disengaged from the bulb mounting portion.
Furthermore, the socket 105 has the relay terminals 109, and therefore there is a problem that the number of contacts increases, so that the reliability of electrical contact of the contacts is lowered. Namely, the supply of electric power from the battery to the bulb 100 is effected via the relay terminals 109, and therefore there are provided the two contacts, and if one of the two contacts should be incompletely contacted, the bulb 100 can not be lighted.